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Bathroom vents terminates to attic. The Inspector recommended that it terminates to the outside. What is the best way to do this. Should I just place the bathroom vent next to the roof vent opening.

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Oops, didn't see the pic when I first answered. That's not a plumbing stack vent, that's a fan vent.

The most code-compliant way to do it would be to give this exhaust its own path to the outside, by cutting a hole in the roof, fitting a vent cap, and running the vent to the cap, attaching and sealing it. You may or may not need a squirrelcage cap (which helps draw air out of the vent), but it will need to be capped to shelter the vent flue from rain. You MAY be able to get away with simply feeding it to the nearest roof vent, depending on the size and design of these, but it won't meet minimum code in most jurisdictions.

Here's why: a vent fan evacuates warm and usually very humid air from your bathroom or kitchen (you're most often venting steam from a shower or from boiling pots/pans). Your attic is an enclosed "cold zone"; it has the same temperature as the outside, which in winter across the northern US will be below freezing. If you exhaust this warm air into the attic, the water will condense onto your rafters and freeze, then thaw, wetting the wood and causing weathering damage, mold and rot over time. Even if it comes out right next to a roof vent, if the air can mingle with attic air, condensation onto wood can still occur.

  • I'm trying to avoid having to cut a whole in the roof. Will it really make much difference if i just extend and place the pipe next to the roof vent. – Hussein Jun 21 '11 at 20:42
  • Like I said in the edited answer, you MAY be able to get away with it, but it's not minimum code because you can still get condensation onto wood and other materials in the attic, which is a recipe for mold, weathering and rot of the interior structure of your house. Trust me, a day spent cutting the hole and fitting a vent, or a couple hundred dollars to have a roofer do it, is pocket change next to the kind of damage you can wind up with after 5-10 years of severe condensation in your attic. – KeithS Jun 21 '11 at 20:46
  • if we installed a solar power attic fan that push air out, would you say it would be ok to point the bathroom vent in the direction of that attic fan so we do not have to make 2 holes in the roof (one for bathroom vent and one for attic vent) – Hussein Jun 22 '11 at 3:02
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    I am not saying it is "ok" and you will not hear me say it, because even with an active mechanism to pull air out, it most likely will not meet minimum code requirements, and it is therefore technically illegal. What I will say it that it may work well enough to be a temporary solution, that improves the situation, but it isn't the proper fix. – KeithS Jun 22 '11 at 14:27
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You could vent out the wall with one of these guys

 Louvered Vent (Louvered Exhaust Vent)

Or out the roof with one of these

 Galvanized Steel Roof Cap (Roof vent cap)

Either way, your inspector is correct. Blowing warm moist air into the attic is probably not the best idea.

It's also not a good idea to vent out the wall too close to the soffit vents, as the exhaust will just be sucked back into the attic through the soffit.

  • Thanks. What are these things called and what do you mean by vent out the wall too close to the soffit vents – Hussein Jun 21 '11 at 21:01
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    Under your eaves, between the outer edge of your roof and the wall of your house, is the soffit. There are usually vented plates or panels in the soffit; these are part of the overall ventilation of your attic. Air comes in through the soffit vents and exits through the roof vents (depending on design and code the roof vents can be louvers in the walls on the sides of the house, capped holes in the top of the roof, and/or an apex vent). If you put your exhaust vent cap too close to the soffit vents, it just gets drawn right back into the attic, condenses, and causes all the same problems. – KeithS Jun 21 '11 at 21:11
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When I replaced a closed box recirculating bath fan with a large exhaust fan, I let the local hardware store owner convince me it was adequate to vent the bath fan into the attic because (he said) “the ridge vent would adequately exhaust all the bathroom air.” BIGGEST MISTAKE WE EVER MADE. By the dry winter season our ceilings all separated from the tops of the walls. Subsequent professional inspectors diagnosed this as “truss uplift syndrome”, a serious structural problem where all of our long established (dry) attic scissor trusses absorbed the humidity being vented into the attic and expanded. This was the start of an irreparable seasonal expansion and contraction of all the attic trusses, depending on the difference between their state and the outdoor humidity level. We converted the bath vent to vent outside the roof and added a whole bunch of additional new attic insulation (per the truss uplift specialists’ instructions), but the damage was done. Years later we’re still dealing with the problem of truss uplift syndrome triggered by venting a bathroom into an established attic that hadn’t had bathroom ventilation previously. NEVER pump humid air into your attic - vent it out of the house.

  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming! – Daniel Griscom Jun 6 at 11:21

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